The present invention relates generally to heat-transfer labels and more particularly to a heat-transfer label including an improved acrylic adhesive layer.
Heat-transfer labels are commonly used in the decorating and/or labelling of commercial articles, such as, and without limitation to, containers for beverages (including alcoholic beverages, such as beer), essential oils, detergents, adverse chemicals, as well as health and beauty aids. As can readily be appreciated, heat-transfer labels are desirably resistant to abrasion and chemical effects in order to avoid a loss of label information and desirably possess good adhesion to the articles to which they are affixed.
One of the earliest types of heat-transfer label is described in U.S. Pat. No. 3,616,015, inventor Kingston, which issued October, 1971, and which is incorporated herein by reference. In the aforementioned patent, there is disclosed a heat-transfer label comprising a paper sheet or web, a wax release layer affixed to the paper sheet, and an ink design layer printed on the wax release layer. In the heat-transfer labelling process, the label-carrying web is subjected to heat, and the label is pressed onto an article with the ink design layer making direct contact with the article. As the paper sheet is subjected to heat, the wax layer begins to melt so that the paper sheet can be released from the ink design layer, a portion of the wax layer being transferred with the ink design layer and a portion of the wax layer remaining with the paper sheet. After transfer of the design to the article, the paper sheet is immediately removed, leaving the design firmly affixed to the article and the wax transferred therewith exposed to the environment. The wax layer is thus intended to serve two purposes: (1) to provide release of the ink design from the web upon application of heat to the web and (2) to form a protective layer over the transferred ink design. After transfer of the label to the article, the transferred wax release layer is typically subjected to a post-flaming technique which enhances the optical clarity of the wax protective layer (thereby enabling the ink design layer therebeneath to be better observed) and which enhances the protective properties of the transferred wax release.
Many heat-transfer labels include, in addition to the layers described above, an adhesive layer (comprising, for example, a polyamide or polyester adhesive) deposited over the ink design to facilitate adhesion of the label onto a receiving article. An example of a heat-transfer label having an adhesive layer is disclosed in U.S. Pat. No. 4,548,857, inventor Galante, which issued Oct. 22, 1985, and which is incorporated herein by reference. Additionally, many heat-transfer labels additionally include a protective lacquer layer interposed between the wax release layer and the ink layer. An example of such a label is disclosed in U.S. Pat. No. 4,426,422, inventor Daniels, which issued Jan. 17, 1984, and which is incorporated herein by reference.
One phenomenon that has been noted with heat-transfer labels of the type described above containing a wax release layer is that, quite often, a degree of hazing or a "halo" is noticeable over the transferred label when the transfer is made onto clear materials. This "halo" effect, which persists despite post-flaming and which may detract from the appearance of the label, is caused by the wax coating around the outer borders of the transferred ink design layer. Hazing due to the wax release layer may also appear in "open-copy" areas of the label, i.e., areas of the label where no ink is present between the adhesive and protective lacquer layers, and also may detract from the appearance of the label.
In addition to and related to the aforementioned problem of hazing, when heat-transfer labels of the type described above are applied to dark-colored containers, the outer wax layer of the label often appears as a whitish coating on the container, which effect is undesirable in many instances. Furthermore, scratches and similar abrasions to the outer wax layer of the label can occur easily and are readily detectable.
Accordingly, to address the aforementioned issues, considerable effort has been expended in replacing or obviating the need for a wax release layer. One such wax-less, heat-transfer label is disclosed in U.S. Pat. No. 3,922,435, inventor Asnes, which issued Nov. 25, 1975, and which is incorporated herein by reference. In the aforementioned patent, the layer of wax is replaced with a layer of a non-wax resin. This non-wax resinous layer is referred to in the patent as a dry release since it does not transfer to the article along with the ink design layer. In a preferred embodiment of the patent, the non-wax resinous layer comprises a thermoset polymeric resin, such as cross-linked resins selected from the group consisting of acrylic resins, polyamide resins, polyester resins, vinyl resins and epoxy resins.
Another example of a wax-less, heat-transfer label is disclosed in U.S. Pat. No. 4,935,300, inventors Parker et al., which issued Jun. 19, 1990, and which is incorporated herein by reference. In the aforementioned patent, the label, which is said to be particularly well-suited for use on high density polyethylene, polypropylene, polystyrene, polyvinylchloride and polyethylene terephthalate surfaces or containers, comprises a paper carrier web which is overcoated with a layer of polyethylene. A protective lacquer layer comprising a polyester resin and a relatively small amount of a nondrying oil is printed onto the polyethylene layer. An ink design layer comprising a resinous binder base selected from the group consisting of polyvinylchloride, acrylics, polyamides and nitrocellulose is then printed onto the protective lacquer layer. A heat-activatable adhesive layer comprising a thermoplastic polyamide adhesive is then printed onto the ink design layer.
Although the above-described wax-less, heat-transfer label substantially reduces the wax-related effects discussed previously, said label does not quite possess the same release characteristics of heat-transfer labels containing a wax release layer. Accordingly, another type of heat-transfer label differs from the heat-transfer label disclosed in U.S. Pat. No. 4,935,300, only in that a very thin layer or "skim coat" of a waxlike material is interposed between the polyethylene release layer and the protective lacquer layer to improve the release of the protective lacquer from the polyethylene-coated carrier web. The thickness of the skim coat corresponds to approximately 0.1-0.4 lbs. of the waxlike material spread onto about 3000 square feet of the polyethylene release layer.
An example of the aforementioned type of heat-transfer label, which has been sold by the assignee of the present application for use in labelling polypropylene bottle caps, comprises a paper carrier web overcoated with a layer of polyethylene. A skim coat is overcoated on the polyethylene layer. A protective lacquer layer comprising vinyl and polyester resins is printed onto the skim coat. An ink design layer comprising vinyl and polyester resins is printed onto the protective lacquer layer. A heat-activatable adhesive layer comprising an acrylic resin, a solvent-soluble chlorinated polypropylene and a plasticizer is printed over the ink design and protective lacquer layers. The acrylic resin is a butyl methacrylate resin, such as ELVACITE.RTM. 2045, which is commercially available from ICI Acrylics Inc. (Wilmington, DE). The solvent-soluble chlorinated polypropylene is commercially available from Eastman Chemical Products, Inc. (Kingsport, Tenn.) as chlorinated polyolefin CP-343-1. The plasticizer is a glyceryl tribenzoate, such as BENZOFLEX.RTM. S-404, which is commercially available from Velsicol Chemical Corporation (Chicago, Ill.).
In commonly-assigned, U.S. Pat. No. 5,766,731, inventors Stein et al., which is incorporated herein by reference, there is disclosed a heat-transfer label that is said to be particularly well-suited for use in decorating styrene-acrylonitrile surfaces and containers. Said label includes a support portion comprising a sheet of paper overcoated with a release layer of polyethylene. The polyethylene layer of the support portion is overcoated with a skim coat of wax. A protective lacquer layer comprising a methyl/n-butyl methacrylate copolymer and a methyl methacrylate copolymer is printed onto the skim coat. An ink layer comprising a polyamide and/or acrylic ink is printed onto the protective lacquer layer. An adhesive layer comprising Eastman CP-343-1 solvent-soluble chlorinated polypropylene, a butyl methacrylate resin and glycerol tribenzoate is printed over the ink design and protective lacquer layers.
In commonly-assigned, U.S. Pat. No. 5,908,694, inventors Makar et al., which is incorporated herein by reference, there is disclosed a heat-transfer label that is said to be particularly well-suited for use in decorating untreated high-density and low-density polyethylene containers. Said label includes a support portion, said support portion preferably comprising a paper carrier web. A wax release layer is overcoated on top of the support portion. A protective lacquer layer is printed onto the wax release layer, the protective lacquer layer comprising a hard polyester or acrylic resin, as well as Eastman CP-343-1 solvent-soluble chlorinated polypropylene. An ink design layer comprising an acrylic ink is printed onto the protective lacquer layer. An adhesive layer is printed over the ink design and protective lacquer layers, said adhesive layer comprising a soft polyamide resin, Eastman CP-153-2 solvent-soluble chlorinated polyethylene, ethylene vinyl acetate and erucamide. The aforementioned patent application also discloses a heat-transfer label that is said to be particularly well-suited for use in decorating untreated high-density polyethylene containers. Said label includes a support portion, said support portion comprising a sheet of paper overcoated with a release layer of polyethylene. The polyethylene layer of the support portion is overcoated with a skim coat of wax. A protective lacquer layer is printed onto the skim coat, the protective lacquer layer comprising a hard polyester resin and an ethoxylated alcohol or a like release agent. An ink design layer comprising a polyamide ink is printed onto the protective lacquer layer, and an adhesive layer of the type described above is printed over the ink and protective lacquer layers.
In commonly-assigned, U.S. Pat. No. 5,932,319, inventors Makar et al., which is incorporated herein by reference, there is disclosed a heat-transfer label that is said to be particularly well-suited for use in decorating treated low-density polyethylene surfaces. Said label includes a sheet of paper overcoated with a wax release layer. A protective lacquer layer is printed onto the wax release layer, said protective lacquer layer comprising a pair of cross-linked polyester resins and a cross-linked vinyl resin. One of the two cross-linked polyester resins preferably comprises a polyester resin of the type commercially available as ViTEL.RTM. 2300 polyester resin and a cross-linking agent in the form of CYMEL 303 hexamethoxymethylmelamine resin. The other of the two cross-linked polyester resins preferably comprises a polyester resin of the type commercially available as ViTEL.RTM. 5545 polyester resin and a cross-linking agent in the form of CYMEL 303 hexamethoxymethylmelamine resin. The cross-linked vinyl resin preferably comprises a vinyl resin of the type commercially available as VAGH vinyl resin and a cross-linking agent in the form of CYMEL 303 hexamethoxymethylmelamine resin.
Other patents and publications of interest relating to the use of heat-transfer labels include U.S. Pat. No. 4,927,709, inventors Parker et al., which issued May 22, 1990; PCT Application No. PCT/US97/11575, published Jan. 8, 1998; and PCT Application No. PCT/US97/11309, published Jan. 8, 1998, all of which are incorporated herein by reference.
As evident from the above discussion, different types of heat-transfer labels have been used to decorate a variety of different container types, including various types of plastic containers, certain metal containers and, as hereinafter explained, certain glass containers.
Historically, glass containers have been pre-treated (typically by the container manufacturer) with a "coating" of oleic acid or stearate, whose function is to enhance the abrasion resistance and lubricity of the containers so as to minimize damage (i.e., scratching, breaking) to the containers during the filling, labelling and shipping processes to which they are later subjected. Such lubricant-coated containers are typically treated, prior to decoration, with a silane adhesion promoter of the type described in U.S. Pat. No. 3,907,974, inventor Smith, which issued Sep. 23, 1975 and which is incorporated herein by reference. The reason for silane treatment is that, in the absence thereof, the adhesive layer of the heat-transfer label does not adhere adequately to the lubricant-coated glass. By contrast, the silane adhesion promoter has two functional groups, one of the functional groups being capable of covalently bonding the lubricant-coated glass and the other functional group being capable of covalently bonding the adhesive layer of the heat-transfer label. In this manner, a covalent bond, albeit through the silane adhesion promoter, is formed between the adhesive layer of the heat-transfer label and the lubricant-coated glass.
Over the last several years, an increasing number of manufacturers of glass containers have begun using polyethylene, instead of stearate or oleic acid, as a lubricant for glass containers. This is because polyethylene has been found to provide glass containers with greater lubricity than is provided by stearate or oleic acid. The increased lubricity provided by polyethylene, in turn, enables the manufacture and use of thinner-walled glass containers--a financial savings to glass manufacturers.
Typically, the application of polyethylene to a glass container is accomplished by spraying a polyethylene emulsion (e.g., DURACOAT polyethylene emulsion, commercially available from Sun Chemical) onto the glass container soon after the container has been formed and while the container is in the process of cooling (e.g., when the container has cooled to about 200-250.degree. F.). The actual amount of polyethylene emulsion sprayed onto the container is typically quite small--on the order of approximately 0.006 mg/container. Moreover, because spraying is the typical method of applying the polyethylene emulsion to the glass container, there will often be a lack of uniformity (or even an occasional bare spot or two) in the polyethylene coating formed on the glass container.
At present, approximately 90% of all glass containers manufactured domestically are treated with a polyethylene lubricant. Polyethylene-coated glass containers, however, cannot be decorated with existing heat-transfer labels due to a lack of adhesion between the heat-transfer label and the polyethylene-coated glass container. Moreover, this lack of adhesion between the heat-transfer label and the polyethylene-coated glass container cannot be ameliorated satisfactorily by silane-treatment of the polyethylene-coated glass container.
In commonly-assigned, U.S. Pat. No. 5,824,176, inventors Stein et al., which is incorporated herein by reference, there is disclosed a heat-transfer label including an adhesive layer comprising an acrylic adhesive resin of the type present in a water-based adhesive emulsion or dispersion. In one embodiment, said label is said to be well-suited for use in decorating silane-treated glass containers of the type subjected to pasteurization conditions, said label including a support portion comprising a sheet of paper overcoated with a release layer of polyethylene. The polyethylene layer of the support portion is overcoated with a skim coat of wax. A protective lacquer layer is printed onto the skim coat, the protective lacquer layer comprising a phenoxy resin. An ink design layer is printed over the phenoxy protective lacquer layer, said ink design layer comprising a polyester/vinyl ink, a polyamide ink, an acrylic ink and/or a polyester ink. The above-mentioned adhesive layer is printed over the ink design layer, any exposed portions of the protective lacquer layer and a surrounding area of the skim coat. According to the above-referenced patent application, a preferred composition for use in forming the aforementioned adhesive layer comprises about 73.4%, by weight, RHOPLEX.RTM. GL-618 acrylic emulsion; about 17.1%, by weight, isopropyl alcohol; about 7.3%, by weight, water; and about 1.5%, by weight, Triton.RTM. X114 nonionic surfactant.
One problem that has been experienced by the present assignee in connection with the manufacture and use of the above-described label is that the aforementioned adhesive layer often does not print satisfactorily upon its underlying layers (particularly onto the exposed portions of the protective lacquer layer and onto the surrounding skim coat area), thereby often resulting in a label transfer having less-than-optimal quality in open-copy areas and around the outer borders thereof. Moreover, such defects are often exacerbated when the label transfer is thereafter subjected to pasteurization conditions.